Lystine tRNA from polyoma and murine sarcoma virus-transformed mouse cells in tissue culture has an extra isoaccepting species not found in normal cells or not found in amounts sufficient to define its presence. The proposed research is to demonstrate whether the extra species is required for the establishment or maintenance of the transformed state. Functional and structural features of the extra species are to be determined and compared with the normal species. Preliminary results also indicate differences between lysyl-tRNA synthetases from normal and transformed cells. The differences are to be further investigated on more purified preparations. The results should lead to a broader understanding of tRNA in general and to a better understanding of the role of tRNA in cellular processes, both normal and abnormal.